Pilot-scale load tests of a combined multilayered geocell and rubber-reinforced foundation

ABSTRACT: This paper describes the reinforcing effects of multiple layers of geocell in combination with rubber–soil mixture layers in sand, and compares their behaviour with that of the multilayered geocell reinforcement alone, using plate loading at a diameter of 300 mm. The plate load tests were performed in an outdoor test pit, dug in natural ground measuring 2000 × 2000 mm in plan and 700 mm in depth. The geocell used in the tests was non-perforated with pocket size 110 × 110 mm² and height 100 mm, fabricated from continuous polypropylene filaments as a nonwoven geotextile. The optimum embedded depth of the first layer of geocell and the vertical spacing of geocell layers were found to be approximately 0.2 times the footing diameter, and the optimum percentage of rubber replacement was found to be around 8% by weight of the soil mixture. Both bearing capacity increase and settlement reduction were highest when multiple layers of geocell and rubber reinforcement were used. Results show that the reinforcements' efficiency decreased as the number of reinforcement layers increased, particularly at low settlement ratios. Higher bearing capacity and lower settlement were achieved by replacing the layers beneath the geocell layers with the rubber–soil mixture. At a ratio of settlement to plate diameter of 2%, the values of bearing pressure were in the ratio 1:2.3:3 for, respectively, the unreinforced installation, the installation with three layers of geocell, and the installation with three layers of geocell and rubber–soil between the layers. The inclusion of the geocell layers reduces the vertical stress transferred down through the foundation bed by distributing the load over a wider area. For example, at the pressure of 550 kPa applied on the soil surface, the transferred pressure at the depth of 510 mm is about 48%, 34% and 27% for the reinforced bed with one, two and three layers of geocell, respectively, compared with the stress in the unreinforced bed. Furthermore, use of the combination of geocell and rubber–soil mixture layers is more effective than use of geocell layers only in reducing the stress transferred downwards. For example, 350 mm beneath a soil surface that carries a stress of 830 kPa, the vertical stress is 15% less when two geocell layers are combined with two rubber–soil mixture layers than when there are only two geocell layers.